Winter preheat using a generator

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Matthew Rogers

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I have a 150 tied down outside in the cold - wish I had the funds for a hangar, heated or not, even with elec would be a plus. What I do have is a small 900 watt harbor freight generator that cost a whopping $99, a 300 watt magnetic oil pan heater, and an electric blanket that I sewed a waterproof cover around.

So my plan is to use the magnetic oil pan heater on the oil sump and wrap the heating blanket over the cowling with a couple of straps. That is about 400 watts of heat and the generator is fine with that load. However, I was thinking about all the waste heat from the exhaust of that little generator. I am trying to get heat - so why waste that.

I tied a length of 4" metal flex duct around the small exhaust pipe on the generator and it pumps out a stream of nicely heated air that I can direct into the cowling to add a bunch more heat with no added expense or energy. The temperature of that exhaust is not high enough that it burns my hand so I don't see any fire risk. It is a two-cycle motor so I guess there will be a little oil smoke.

See any issues or has anyone used exhaust to heat their aircraft before? If I am lucky, my airport will be melted out on Thursday so I can fly it out of the grass strip and off to its winter home. It is going to be a low of 10-25 (forecasts differ widely). I was down in Florida during this storm and the other owner let his BFR expire and decided not to do anything about the snow situation!

I have not used this setup yet, so don't go calling "you're gonna die", or "you must already have killed yourself". Just spitballing about using the extra heat from the exhaust to make it more efficient. I can even take this generator in the plane if necessary as the whole setup weighs 30 pounds.
 
Some people preheat using a camp stove that burns a variety of fuels (including avgas in a pinch) and some ducting to direct the exhaust into the cowl. I would think that a modern two-cycle engine wouldn’t put out much worse exhaust than that. But maybe test it through cheese cloth or something else to see how oily the exhaust is. The last thing an airplane engine needs is more oil being deposited on and around it.
 
I don't have a generator and my last 2-stroke was a dirtbike….but does the exhaust have a lot of moisture in it?
 
I also wonder, does your generator have enough power to run the blower of the torpedo style propane heaters? A guy at our airport preheats his plane that way (but has hangar electrical). I don't know how long he runs it but it would seem you could show up, set that up and really heat it up good over about an hour or so. Maybe you could even get warm air into the cabin.
 
I know that there are the combination heaters using either 12v or 120v blowers, batteries or cords, and propane, but now that is another piece of equipment and another tank. I am trying to keep it simple and quick.

I did keep my hand in the exhaust for a while and once warmed up there is no smoke and I didn’t feel anything on my hand as far as residue so I think it will be less than the airplanes exhaust.
 
Couple of problems: 300 watts isn't much. Also, a magnet will not stick to a plane's oil pan. I'd consider a blower heater with some ducting...
 
tawood said:
Couple of problems: 300 watts isn't much. Also, a magnet will not stick to a plane's oil pan. I'd consider a blower heater with some ducting...
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There are plenty of inexpensive oil pan heaters available on Amazon and Ebay. $20 bucks and you've got one. Glue it on, and that'll work fine. If the generator has sufficient power, you could add a blow drier or a cube heater that blows through the cowl inlets or up through the air exit under the airplane.
 
kyleb said:
There are plenty of inexpensive oil pan heaters available on Amazon and Ebay. $20 bucks and you've got one. Glue it on, and that'll work fine. If the generator has sufficient power, you could add a blow drier or a cube heater that blows through the cowl inlets or up through the air exit under the airplane.
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If its glued on, an A&P has to do it to be legal...
 
Oh, guess I forgot that the O-200 oil pan is aluminum. I never tested but figured that all oil pans were steel.

300 watts is not much, but also another 100 watts and some insulation in the heated cowl blanket and also the exhaust heat blowing up onto the engine. That is the point of the exhaust ducting. The exhaust question is the entire point of the post. I would assume that the generator is no more than 30% efficient at converting gas into electricity so that 400 watts of electric equals 800 more watts of waste heat.
 
I use a generator with a E-Z heat oil pan heater from 10F and above. Preheat for 3 hours before a flight. Below 10F I add my red dragon heater for 30 minutes in addition to the generator and E-Z oil pan heater.

Winter in AK means short daylight hours. I start my preheat at 6am and am good to go by 8:30/9:00am,,,:)
 
Why not use the exhaust heat AKBill? I just want to know your thinking.
 
Matthew Rogers said:
Why not use the exhaust heat AKBill? I just want to know your thinking.
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I could be 100% wrong at my thinking, but here goes. My thought are you are introducing a potentially corrosive substance to the engine compartment.

And yes I at times use a red dragon which is essentially a weed burner with a fan but I think the type of fuel produces a less corrosive vapor. Just my thoughts.
 
90% of my preheat is with a generator and an E-Z Oil pan heater..
 
One thing to note. I had an issue with the generator last year, it ran about 1.5 times faster because the fuel governor failed. Voltage of my generator is controlled by the speed of the engine. It sent about 180V instead of 110V to the oil pan heater and fried the oil pan heater. I posted last year on POA....:(
 
Clip4, I can’t tell if that is sarcasm, but the idea actually seems reasonable. You could easily heat the oil in the back of the car using the oil pan heater (starting at a warm 70 degrees already). That circulates 100 degree plus oil around the engine on the first few cranks. I have to change my oil anyway so perhaps I’ll just do this flight using new oil. I think I have an old metal gas can with a spout that I could use as a container.

AKBill, I guess I’ll have to look up if there is anything corrosive in the exhaust. There will be a little bit of water, but that will also evaporate away as the engine warms up and the huge amount of airflow in flight.
 
Maybe just a data point and not necessarily an option for you. I now have a remote heat wifi switch. It also gives me current draw and power consumption. My tannis heater on a O-470 is drawing 3.6amps and right around 430watts. So if a STC'd engine heater was an option your 900W generator should easily run it and that would give you oil and cylinder head heat. I don't know how long it needs that heat for though? That is what's nice about a propane + blower: Lots of BTU's. I can easily put my small propane heater and tank in the trunk of a car. Now a generator...probably not. And all the ducting to use a propane heater would also take up space in the car or truck.
 
Clip4 said:
I would opt to drain the oil into a 5 gallon metal can after each flight and refill the sump with warmed oil.
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Weren't they doing this during the WWII and other places when it is really cold? Bring the oil in with you at night. And some diluted the oil with some fuel to get it started?
 
Better choice-
75watt silicone heat pad attached to the sump with RTV. Run concurrently with a Zero Start Little Buddy heater (electric heat w/fan). Great combo. Used it myself for many years until I went with Reiff.

https://autoplicity.com/10052460-ph...6U4OSvvHFN_oXesQjWVut_CBBpVIFBnxoCNg8QAvD_BwE

No tip switch on a Little Buddy. Easy to place inside an oil door or do like I did and attach to the engine mount with adel clamps.
 
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Matthew Rogers said:
Clip4, I can’t tell if that is sarcasm, but the idea actually seems reasonable. You could easily heat the oil in the back of the car using the oil pan heater (starting at a warm 70 degrees already). That circulates 100 degree plus oil around the engine on the first few cranks. I have to change my oil anyway so perhaps I’ll just do this flight using new oil. I think I have an old metal gas can with a spout that I could use as a container.

AKBill, I guess I’ll have to look up if there is anything corrosive in the exhaust. There will be a little bit of water, but that will also evaporate away as the engine warms up and the huge amount of airflow in flight.
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Either method you use you still run the risk of frosted plugs. Yes, exhaust is corrosive.
 
Well, the backup plan is a heat gun on low power run into the same metal flex duct. I guess I'll just save the exhaust idea for an emergency or some super cold day where I have no other choice and need to get out of there. I could try to rig up a heat exchanger tube where the exhaust gas heats the duct through which the heat gun air is flowing, thereby increasing the efficiency and saving some of that waste heat but not directing the exhaust directly onto the plane. something as simple as a 4" tube inside of a 6" tube.
 
Heat gun? Try a blow dryer and just stick it inside the cowl. Your big error will be not heating for a long enough time.
 
Build a heat exchanger, exchange the hot exhaust gas heat with ambient air, blow the newly heated ambient air into the cowl :). The engineer in me likes the idea of using the waste heat, but I think it's just more headache than it's worth.
 
Sinistar said:
Weren't they doing this during the WWII and other places when it is really cold? Bring the oil in with you at night. And some diluted the oil with some fuel to get it started?
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Yes they were. BUT it is a lot easier when the engine is a radial with a dry sump. -Skip
 
If it were me...put something over electric blanket, heat 6 quarts of oil inside car under floorboard heater, maybe tape or zip tie your magnetic heater. Dont overthink it. 10-25 isn't that cold
 
I think running 2 cycle exhaust into an engine compartment would create a big mess from corrosion, general oil crude contamination, and overall stink.
 
Stewartb said:
Red Dragons are my least favorite heat choice
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I agree, I use it from 0 to 10F. Only do 30 min with the Red Dragon, enough to warm the cylinders. I guess there are better ways to preheat. The local FBO does not have a preheater now.,,:( In the past I would call them up and 30 min later engine was happy warm.
 
One last idea - simple and no fumes. The flex duct gets very hot and has lots of surface area so it makes a great heat exchanger. If I just lengthen it and run a loop of it up into the bottom of the cowl and back out, it will add a lot of heat and then still direct the exhaust outside the plane. Like a big radiant heat source. Not quite as efficient as using all the exhaust, but eliminates all the issues brought up and uses no more fuel, money, or time.

Guess I am done here. Thanks for being up the possibility of corrosion. I’ll post results after a few uses. I have a non contact thermometer gun and I’ll take some measurements. Might even stick a thermocouple down into the oil sump.
 
Sinistar said:
I also wonder, does your generator have enough power to run the blower of the torpedo style propane heaters? A guy at our airport preheats his plane that way (but has hangar electrical). I don't know how long he runs it but it would seem you could show up, set that up and really heat it up good over about an hour or so. Maybe you could even get warm air into the cabin.
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Don't use a torpedo heater.
https://www.pilotsofamerica.com/com...ds-how-to-make-your-engine-last-ground.55073/
 
Matthew Rogers said:
...AKBill, I guess I’ll have to look up if there is anything corrosive in the exhaust. There will be a little bit of water, but that will also evaporate away as the engine warms up and the huge amount of airflow in flight.
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Of course it is corrosive. The exhaust contains more than water vapour. It also contains carbon based combustion byproducts, including CO2. That means there will be carbonic acid (H2CO3) in that stream. It's the reason exhaust systems corrode from the inside out.
 
Matthew Rogers said:
One last idea - simple and no fumes. The flex duct gets very hot and has lots of surface area so it makes a great heat exchanger. If I just lengthen it and run a loop of it up into the bottom of the cowl and back out, it will add a lot of heat and then still direct the exhaust outside the plane. Like a big radiant heat source. Not quite as efficient as using all the exhaust, but eliminates all the issues brought up and uses no more fuel, money, or time.

Guess I am done here. Thanks for being up the possibility of corrosion. I’ll post results after a few uses. I have a non contact thermometer gun and I’ll take some measurements. Might even stick a thermocouple down into the oil sump.
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Be cautious and don’t burn your cowl or blister any paint wherever that duct makes contact with anything. Good luck!
 
Don't they make a dipstick heater that would at least warm the oil in lieu of the oil pan heaters? I'd think that combined with a engine blanket/small ducted electric heater would be more than suffucient.
 
Preheating has two functions. It reduces wear on cold engine parts and it makes the engine easier to start. Choosing the right oil for the temperature solves most of the first part. That’s why Lycoming says preheat below 10* and Continental says 20* assuming you use the correct oil. As for ease of starting? Heating the oil allows the engine spin faster and with less resistance. Heating cylinders improves the cylinder’s ability to fire. All preheat is a balance of BTUs in and time. If all you do is heat the oil you still run the risk of frosting your plugs. Do that and your day is over, at least in the north where winter days are short. Heat the cylinders only and your engine may fire right up and you can sit and wait... wait... wait for oil pressure to appear on your gauge. The smart approach is to use a balanced heat system and/or enough time with lesser systems to heat soak the entire engine to a useful starting temperature. Some of us do it regularly and have learned what works and what doesn’t. You wanna know what works? Pay attention to those who already went through the learning curve.
 
D6FAA1D9-422F-42E3-9383-ABC879D293F0.jpeg A Little Buddy is the most useful heater you occasional users will ever find. 900w heat with a circulation fan. No tip switch. All metal construction. Overtemp shutoff built in. Mine rode attached to my engine mount for several years before I removed it and it still works perfectly. It takes a long time to heat oil this way so if you want faster heat-up add a 75w silicone heat pad to the sump and you’ll have a very useful system. And yes, I use a 1000w generator. Always have. Still do.
 
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